Steel dome to contain oil leak will be 'ready in days'

As BP raced to complete construction of a steel dome it intends to lower over oil leaks almost a mile below the surface of the sea in the Gulf of Mexico, the Governor of Florida warned that his state may sue the London-based company. "It is certainly in the realm of possibility," Charlie Crist said.

With technology that looks more Heath Robinson than 21st century, engineers for BP put the final touches to the first of the 90-tonne boxes, called a cofferdam, at Port Fourchon, Louisiana.

The idea is to contain the oil as it spews from a broken pipe and then siphon it out through what would effectively be a giant straw to a tanker ship, the Enterprise, waiting above. Officials hope to have it in place within a few days. A team of 25 people is working non-stop on the funnel, which is being built near Port Fourchon by a specialist company, Wild Well Control.

But with BP warning that doming at that depth has never been attempted before, there was no let-up in preparations for the vast slick offshore. More than 10,000 volunteers were mobilising all along the Gulf Coast, laying down booms and deploying clean-up crews.

President Barack Obama vowed to help the region overcome the economic impact of the disaster. "We are committed to preventing as much of the economic damage as possible by working to contain the impact of this potentially devastating spill," he said. Fisheries have already shut down.

New Orleans, meanwhile, was slowly becoming headquarters for the second time in five years to teams of lawyers specialising in post-disaster litigation. Thousands of claims have already been filed against BP, mostly to do with loss of income in the wake of the disaster.

"There is a claims process that is very clear and it has been posted publicly," Lucia Bustamante, the external affairs director for the company, advised potential plaintiffs. "What I can tell you is to keep proper documentation of everything. You are going to need it."

Attempts by BP to activate a valve at the seabed to shut down the leaks have remained unsuccessful and the leak rate was still being put at about 210,000 gallons a day. The company said that work on drilling a relief well had started. But it may be three months before the new boreholes will allow engineers to clot the first well with mud and concrete and stop the leaks.

"The expansiveness of it is just incredible," Governor Crist said after viewing the slick from the air for the second time. "It just continues to grow. That's very distressing. We're just trying to do everything we can to protect our state." He called the situation in the Gulf an "unprecedented crisis" for the Sunshine State.

While several days of storms had impeded attempts to spray the slick and burn off some of the oil, the inclement weather may, in fact, have had a washing-machine effect of dispersing some of the oil by natural means. "It was actually a huge help for the coast," said Ed Overton of Louisiana State University. "It was mother nature coming to our rescue for a few days."

Much calmer weather has allowed the Coast Guard to redeploy booming and burn-off crews. The slick, however, has also begun to show signs of reorganising. Where it eventually strikes shore depends also on currents. The clockwork loop current in the Gulf could soon catch the slick and convey it towards the ecologically vulnerable Florida Keys and from there round to Miami and the eastern seaboard of the state.

Senior executives of BP were meanwhile turning their eye to politics and Washington where they can expect to be grilled by members of Congress in the coming days and weeks over the circumstances of the disaster.

Scrutiny was also turning to the government department that issues leases and permits for offshore drilling. Darrell Issa, a member of the House Oversight and Government Reform Committee, said he would investigate whether BP was improperly awarded safety certificates by the Interior Department.

The spill has drained $32bn (£21bn) from the stock market value of BP, the world's third-largest oil company. BP made $6bn in the first three months of this year.